The present invention relates to a lubricating oil composition and, more particularly, to a lubricating oil composition which is bearing oil, gear oil or hydraulic oil exhibiting excellent extreme pressure property, seizure resistance and wear resistance and to a refrigerator oil composition which is stable and exhibits excellent extreme pressure property, seizure resistance and wear resistance under various refrigerants.
The role expected to be played by lubricating oil is to make movements of frictional portions smooth. To play this role, extreme pressure agents, antiseizure agents and antiwear agents are added to a base oil of lubricating oil and the extreme pressure property, seizure resistance and wear resistance are improved.
Recently, as facilities such as apparatuses and machines are becoming smaller and exhibiting higher performance, lubricating portions are subjected to much higher loads and speeds. Therefore, a lubricating oil is required to exhibit much more improved properties such as much more improved extreme pressure property; seizure resistance and wear resistance.
Various types of refrigerants are used in compression-type refrigerators. For example, hydrofluorocarbons whose typical examples include 1,1,1,2-tetrafluoroethane (R-134a) and fluorocarbons are used to prevent the environmental pollution such as the ozonosphere destruction and carbon dioxide, ethers, ammonia and hydrocarbons are used to prevent global warming and to secure the safety of the human being. Therefore, it is required that lubricating oil for compression-type refrigerators exhibit more improved extreme pressure property, seizure resistance and wear resistance and remain stable under the special atmosphere of these refrigerants.
The present invention has been made under the above circumstances and has an object of providing a lubricating oil composition which exhibits excellent extreme pressure property, seizure resistance and wear resistance and is advantageously used as bearing oil, gear oil, hydraulic oil and refrigerator oil.
The present invention has another object of providing a refrigerator oil composition which is stable and exhibits excellent extreme pressure property, seizure resistance and wear resistance under various refrigerants used for refrigerators.
As the result of extensive studies by the present inventors, it was found that the above object could be effectively achieved by using a lubricating oil composition comprising a specific cyclic organic phosphorus compound. The present invention has been completed based on the above knowledge. The present invention can be summarized as follows:
(1) A lubricating oil composition which comprises a base oil and at least one compound selected from cyclic organic phosphorus compounds represented by following general formula (I): 
xe2x80x83wherein Z represents hydrogen atom, an alkyl group, a cycloalkyl group which may be substituted with at least one of alkyl groups having 1 to 12 carbon atoms and hydroxyl group, an aryl group which may be substituted with at least one of alkyl groups having 1 to 12 carbon atoms and hydroxyl group or an alkyl group substituted with an aryl group which may be substituted with at least one of alkyl groups having 1 to 12 carbon atoms and hydroxyl group, X1 and X2 each independently represent a halogen atom or hydroxyl group and p and q each represent an integer of 0 to 3.
(2) A lubricating oil composition described in (1), wherein the cyclic organic phosphorus compound is a compound expressed by following formula (II): 
xe2x80x83a compound expressed by following formula (III): 
xe2x80x83or a compound expressed by following formula (IV): 
xe2x80x83wherein tert-Bu represents tertiary-butyl group.
(3) A lubricating oil composition described in any one of (1) and (2), wherein a content of the cyclic organic phosphorus compound is 0.001 to 5% by weight based on an amount of the composition.
(4) A lubricating oil composition described in any one of (1) and (2), wherein the base oil is at least one oil selected from purified mineral oils, alkylbenzenes, poly-xcex1-olefins, polyalkylene glycols, polyvinyl ethers, polyesters and polycarbonates.
(5) A lubricating oil composition described in any one of (1) to (4), which further comprises at least one agent selected from metal salts of carboxylic acids and phosphorus-based extreme pressure agents in an amount of 0.001 to 5% by weight based on an amount of the composition.
(6) A lubricating oil composition described in any one of (1) to (5), which further comprises phenolic antioxidants.
(7) A lubricating oil composition described in any one of (1) to (6), which further comprises acid scavengers.
(8) A lubricating oil composition described in any one of (1) to (7), which is bearing oil, gear oil or hydraulic oil.
(9) A lubricating oil composition described in any one of (1) to (7), which is refrigerator oil.
(10) A lubricating oil composition described in (9), wherein a refrigerator which uses the refrigerator oil is a compression-type refrigerator using a refrigerant containing fluorine, carbon dioxide, ammonia, an ether or a hydrocarbon as a refrigerant.